Does anybody know the size and pitch for the thread on a A2 flash-hider?
Yes and no. A muzzle brake is an attachment to the barrel of a firearm that redirects propellant gases to counter recoil and unwanted rising of the barrel during firing. This effectively reduces the amount of muzzle rise and kickback experienced by the shooter.
A flash suppressor, on the other hand, is a device attached to or built into the barrel of a firearm that reduces visible light and infrared light (heat) signatures caused by firing the weapon. It does this by trapping propellant gas in small pockets or chambers around the edge of the muzzle device which in turn cools it down and prevents it from emitting light.
So, a muzzle brake can help reduce recoil while a flash suppressor can help to conceal your position when firing. But, a muzzle brake will not reduce the flash signature of your firearm and a flash suppressor will not reduce recoil.